This invention relates to a particular method and apparatus for starting and maintaining an arc in a plasma type gas arc cutting or welding system.
Plasma cutting systems utilize a high speed stream of hot ionized gas to melt and cut electrically conductive metals. Such systems operate by forcing a gas such as compressed air through a narrow orifice at the end of the plasma torch. Plasma gas first flows between the electrode and cutting nozzle inside of the plasma torch. In order to ignite this gas inside of the torch head, a high voltage spark must be generated between the electrode and the cutting nozzle to form a pilot arc. Once this spark is generated, the main plasma power supply maintains the resulting pilot arc which can then be transferred as a main arc to the metal to be cut. Thus, to start the cutting process, a weak pilot arc is needed to generate a path for electricity to be conducted from the plasma torch to the metal under cut.
Typically in a plasma cutting system some form of high voltage, high frequency pulse is used to generate a spark inside the torch to ignite the pilot arc. This is normally accomplished by the use of a high voltage transformer, a set of spark gaps and a high voltage coupling coil. Other systems use a high frequency, high voltage solid state device to generate the pilot arc.
These prior art systems generate large amounts of high frequency, high voltage electromagnetic waves that can cause electrical interference with other electrical equipment in the area. The spark gap system also has the disadvantage of requiring periodic maintenance to adjust the gap distance and/or replace the points forming the spark gap.
In order to minimize or overcome problems such as the above this invention has been made.